Cathode and method of making same



May 31, 1960 w, NELSON 2,939,033

CATHODE AND METHOD OF MAKING SAME Filed Oct. 22, 1957 INVENTOR. Walter E. Nelson Attorney United. States Patent CATHODE AND METHOD OF MAKING SAME Walter E..Nelson, San Jose, Calif., assignor to Varian Associates, Palo Alto, Calif, a corporation of California Filed Oct. 22, 1957, Ser. No. 691,662

8 Claims. (Cl. 313-346) This invention relates, in general, to emitters or cathodes for use in electron discharge devices and more particularly to a novel cathode having uniform emission and long life, and to a method for producing the same, said cathode being especially useful in high power beam tubes such as, for example, klystron amplifiers and the like.

Heretofore, cathodes of the type to which the present invention relates have been formed by sintering or spot welding a metallic mesh onto a cathode base or button. After sintering, a suitable cathode emitting substance, such as barium strontium powder suspended in a binder liquid, was applied to the mesh. The binder containing the emitting substance filled up the spaces. in the mesh and, when dry, the residue formed the emitting surface.

The disadvantages of the product of this prior art process results from the fact that the mesh could not, as a practical matter, be uniformly sintered or spot welded onto the cathode button. Consequently, when the cathode was heated, there was greater heat conductivity in the immediate area of the sintering or spot welding hence forming hot spots and correlative cold spots on the emitting surface. This effect manifested itself in beam distortion and shortened life, the former resulting from a nonuniform emission, and the latter resulting from undesired arcing between the anode and cathode causing cathode particles to be chipped out in the immediate area of the cold spots.

It is, therefore, the principal object of this invention to provide a novel cathode and method for producing the same, the said cathode having uniform thermal conductivity from the cathode base member to the emitting substance, and a retaining matrix capable of containing relatively large deposits of cathode emitting substance, hence resulting in uniform emission and extended life.

One feature of the present invention is a novel cathode comprising a base member, and an aggregate of projecting stalagmitic or cone shaped elements fixed to the base member, said stalagmitic elements serving as a retaining matrix for deposits of cathode emitting substance in relatively substantial quantities, thereby enhancing the useful life of the cathode.

Another feature of the present invention is the novel method of assembling a cathode in a polarizing force field such that cathode particles are caused to form into projecting stalagmitic or cone shaped elements with respect to the cathode base or button and are in physical contact with said base or button thereby providing uniform and efficient heat transfer to the emitting substance.

2,939,033 Patented May 31, 1960 wherein cathode emitting substance suspended in a binder liquid is applied to the stalagmitic surface formed by the stalagmitic elements, the said emitting substance suspended in a binder liquid completely filling the retaining matrix formed by the spaces between the stalagrnitic elements thereby causing a relatively substantial quantity of emitting substance to be deposited whereby the useful life of the cathode isenhanced.

A further feature of the present invention is the novel method of achieving efficient thermal conductivity between the cathode base member and the emitting substance via the stalagmitic elements wherein the particles forming said stalagmitic elements are sintered together into a coherent rigid thermally efiicient mass.

A still further feature of the present invention is the novel method of sintering the stalagmitic elements to Another feature of the present invention is the prothe base member such that the aggregate of these stalag mitic elements form a rigid, thermally eflicient retaining matrix for relatively substantial deposits of emitting substance.

These and other features and advantages of the present invention will be more apparent after -a perusal of the following specification taken in connection with the accompanying drawings wherein,

Fig. l is a schematic cross sectional view depicting the novel method and apparatus of the present invention,

Fig. 1a is an enlarged schematic cross sectional view of a portion of the structure of Fig. l with the cathode emitting substance removed and is delineated by line 1a of Fig. l, and

Fig. 2 is an enlarged schematic cross sectional view of a portion of the structure of Fig. 1 delineated by line 1a.

Referring now to the drawings, a cathode base or button 1 as of, for example, nickel is placed in a polarizing force field such as, for example, a magnetic field produced by a DC. current carrying coil 2 surrounding the button and in axial alignment therewith. The magnetic lines of force are therefore parallel to center line C which passes axially through the cathode base 1. The upper surface 3 of the button 1 is coated with a thin layer of binder liquid such as, for example, a nitro-cellulose lacquer, commercially available as RCA 33D109 binder. When the binder is partially dry, cathode particles as, for example, nickel powder, carbonyl nickel or tungsten nickel are sprinkled onto the upper surface 3 of the cathode base 1. The polarizing magnetic field causes these particles to form stalagmitic or cone shaped elements 4 (see Fig. 1a). These stalagmitic elements absorb the partially dry binder. The sprinkling of cathode particles continues until the entire surface 3 of the button 1 is evenly covered with these stalagmitic elements. The height of these stalagmitic elements varies with the requirements of design and can be increased by continuing the sprinkling process.

When the desired height is achieved, the sprinkling process ceases and the binder liquid is permitted to dry in a drying atmosphere for a few minutes until sutficiently hardened so as to support all of the stalagmitic elements 4 independent of the polarizing magnetic field thereby forming a rigid retaining matrix for a large deposit of emitting substance. The magnetic field is then removed. The button 1 is then heated in an oven at a temperature of about 1350 C. for about 30 minutes until sintering takes place at the points of contact between the bases of the stalagmitic elements 4 and the cathode button 1 along the surface 3 and until sintering likewise takes place between touching cathode particles forming the stalagmitic elements.

When the desired sintering has taken place, the button 1 is removed from the oven. Undesired surface protrusions or peaks of the highest stalagmitic elements are depressed with a radius tool until all undesired peaks are eliminated. A cathode emitting substance is then applied to the retaining matrix formed by the plurality of the stalagmitic elements. This substance can be any suitable cathode emitting substance such as, for example,

barium strontium, suspended in a liquid such as, for

example, amyl acetate. After application of the cathode emitting substance the cathode is exposed to a drying atmosphere until dry. The procedure of application of cathode emitting substance and drying is repeated until all the space between the stalagmitic elements 4 are compl'etely filled in (see Fig. 2).

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An electron emitting cathode including a base member, a plurality of rigid projecting cone-shaped elements fixed at their wide ends upon said base member, said projecting elements comprising an aggregate of cathode particles, and a relatively substantial deposit of cathode emitting substance surrounding and retained by 'said projecting elements.

2. An electron emitting cathode including a base member, a plurality of rigid cone-shaped elements fixed at their Wide ends upon said base member and extending therefrom, said elements comprising a formed aggregate of cathode particles, said elements serving as a retaining matrix for a relatively substantial deposit of a cathode emitting substance, and a relatively substantial deposit of cathode emitting substance completely occupying the retaining matrix thus enhanching the useful life of the cathode.

3. An electron emitting cathode according to claim 2 wherein said cone-shaped elements are sintered directly to said base member thereby achieving uniform thermal conductivity between said base member and said stalagmitic elements.

4. An electron emitting cathode according to claim 2 wherein said cone shaped elements are formed by sintering together a plurality of cathode particles to form a coherent solid mass in the form of a retaining matrix thereby achieving rigidity and uniform thermal conductivity throughout said cone-shaped elements.

5. The method of assembling an electron emitting cathode of the type having a cathode base member and an emitting substance coupled to said base member comprising the steps of placing the base member in a polarizing force field, applying cathode particles to the base member, the cathode particles under the influence of the force field forming into a plurality of stalagmitic elements on the base member, securing the stalagmitic elements to the base member and securing adjacent particles forming the stalagmitic elements to each otherto produce a rigid matrix whereby the thermal conductivity of the stalagmitic elements thus formed is substantially uniform and adhering a cathode emitting substance to the stalagmitic elements.

6. The method according to claim 5 including the steps of applying a binder means to the plurality of stalagmitic elements, expo-sing the binder means to a drying atmosphere until the binder is sufficiently hardened so as to sustain erection of the stalagmitic elements independent of the polarizing field, and removing the polarizing field.

7. The method according to claim 5 wherein the step of securing the stalagmitic elements'to the base member and the step of securing adjacent cathode particles of the stalagmitic elements to each other comprises the steps of sintering the stalagmitic elements to the base member, and sintering adjacent cathode particles forming the stalagmitic elements to each other.

8. The method according to claim 5 wherein the step of adhering the emitting substance to the plurality of stalagmitic elements comprises the steps of applying cathode emitting substance suspended in a binder liquid to the retaining matrix formed by the stalagmitic 'elements thereby causing the cathode emitting substance to completely occupy the retaining matrix, and exposingthe binder liquid to a drying atmosphere for a period of time sufficient to cause the binder liquid to harden thereby causing the cathode emitting substance to be permanently deposited. 

